Grinding disk



p 1937- T. L. F. LARSSON 9 GRINDING DISK Filed Dec. 5, 1934 W/ TNE 5 3 577/1/05 1. FZFRJ'J'O/V (TJWWR H. ca

Patented Sept. 14, 1937 UNITED STATES PATENT OFFICE cnmnmc. msx

Application December 5, 1934, Serial No. 756,137 I 3 Claims.

This invention relates to a bonded abrasive disk and especially to asector type of grinding disk such as a, grinding wheel which presents anextensive fiat grinding face.

Grinding disks as used heretofore for performing abrading operationswith their flat annular faces have usually comprised homogeneous,unitary, bonded abrasive bodies, such as a flat faced grinding wheelwhich is cemented or otherwise suitably fastened to arigidrotatable-support, whereby the entire fiat face of the abrasive body maybe employed for a grinding operation. Grinding disks of this type areadapted for various heavy duty grinding operations such as, for example,dry grinding the ends of large coil springs. However, much difiicultyhas been encountered in suitably securing such an abrasive disk to itsbacking plate with sufiicient tenacity to withstand the various heavyduty grinding operations to which this particular shape and type ofgrinding disk is especially adapted.

Heretofore in the manufacture of grinding disks of this general type,the abrasive bodies.

' often become loosened from their metal supporting plates or variousserious structural cracks and ruptures frequently developed within thebonded abrasive body itself. Furthermore, due to the excessive changesoccasionedin such a grinding disk during a grinding operation, it hasbeen found that a large grinding disk is incapable of withstanding aheavy duty grinding operation. It has also been found that many of thesedisks are unsuited for dry grinding operations since their operativesurfaces are rapidly brought to a high temperature due to the frictionof grinding and this high temperature on the operative wheel, face isattained long before other wheel portions experience any appreciabletemperature change. As a result, the operative wheel face tends toexpand at an extremely rapid rate, while other portions of the grindingwheel and its rigid backing support tend to resist this expansion,thereby resulting in uneven internal stresses which usually cause wheelbreakage. Furthermore, the coefiicients of expansion of the bondedabrasive disk and the metal backing support are so unrelated that theyexpand to greatly different extent due to heat of grinding andfrequently cause the bonded abrasive body and its metal backing memberto break apart during a grinding operation, thereby subjecting themachine operator to considerable danger and often resulting in spoilageof the work and damage to the grinding machine.

and sudden temperature.

' In attempts to surmount these difliculties and compensate for theexpansions and contractions of an operative wheel face duetofrictionalheat of grinding, various types of abrasive disks have beencomposed of a large number of spaced seg- 5 ments or sectors fastenedtogether in annular form. However, these various attempts have provedunsatisfactory. For example, various devices, such as chucks,'have beenutilizedto clamp a plurality of spaced abrasive blocks to a rotat- 10able rigid support so-that each of the blocks may be continuously movedthrough the same circular path and thus cooperate to provide a grindingoperation. These chucks have been unsatisfactory in many respects, sincethey are cumber- 15 some, expensive devices and the abrasive blocksthemselves are relatively narrow, so that the total operativegrindingsurface only includes a very small portion of the area within thecircular path through which the blocks are rotated. Abrasive blocks ofthis type must be carefully shaped and in many instances they must beccmented to precisely shaped clamping members so that they -may beaccurately seated within their respective chuck jaws, thereby providinga 2 construction which is not only expensive but also difiicult and slowto assemble.

It has also been proposed to secure a plurality of abrasive sectors on arotatable metal backing plate by means of suitable clamping devices,such as nuts which are embedded within the rear face of each wheelsector and engaged by bolts passing through the backing plate, wherebythe sectors may be rigidly secured in desired grinding position.However, constructions of this type 35 have usually provedunsatisfactory for heavy duty grinding operations since the clampingnuts tend to tear loose from their embedded positions. Furthermore,these embedded nuts also cause a considerable portion of the abrasivedisks to be 40 wasted since they preventutilizing a large portion of thelower part of each grinding sector for an abrading operation, therebymaking it impossible to employ all of theavai-lable abrasive materialfor a grinding operation. 45

The principal object of this invention is to overcome the inherentdisadvantages of prior grinding disk constructions and to provide asector type of grinding disk capable of heavy duty grinding operationsand which may be easily and 50 {inexpensively manufactured andpermanently .s. timed to a rigid backing support as an integral unittherewith in such a manner that all of the abrasive material maybeemployed for :a grinding operation and wherein uneven expan- I 5 sionsoccasioned within the disk due to sudden temperature changes may becompensated for.

In the drawing which illustrates this invention and in which likenumerals indicate like parts:

Fig. 1 shows a plan view of a grinding disk embodying my invention;

Fig. 2 is a sectional view taken approximately along line 2--2 of Fig.1; and

Fig. 3 shows a modified form of my invention.

In accordance with this invention, I have pro vided a sector type ofbonded abrasive grinding disk having a plurality of spaced bondedabrasive segments or sectors which are suitably shaped and assembled toprovide an extensive flat annular grinding face including the majorportion of the area within the disk periphery. To facilitate expansionsand contractions of the operative grinding face, the sectors areassembled in spaced relation to each other and they are cementedtogether as well as to a rigid backing support by means of suitablevulcanizabie compounds, such as rubber, which may be resilient orslightly deformable between the adjacent opposed sectors to compensatefor the individual expansions and contractions of each sector. Thisconstruction is provided to relieve the operative grinding portion ofeach sector of its stresses without permitting them to be transmitted toadjacent sectors and thereby accumulate and tend to cause rupture of thegrinding body. It will be 'appreciated, however, that the cementingmedium also serves to so locate the sectors relative to each other thatthey form an integral, substantially unitarygrinding disk having asubstantially continuous flat grinding face. In the preferred type of myinvention, the abrasive sectors are integrally secured to a rigidbacking member, such as a metal supporting plate, by means of a layer ofvulcanized hard rubber. Furthermore, this invention provides a highlyefficient type of grinding disk wherein all of the abrasive material maybe employed for grinding operations. In fact, it has been found that agrinding disk of this type may be appreciably stronger than a unitarygrinding disk of the same grade and shape when used for certain heavyduty grinding operations, since the internal stresses and strains withinthe grinding member are relieved within each wheel sector and hence haveno opportunity to accumulate sufficiently to produce disruptive forces.

It has been found that rubber containing 20% or more of combined sulphurby weight which is vulcanized to a hard, tough condition of the generalnature of ebonite or vulcanite, and commonly referred to as "hardrubber, provides a highly eflicient and tenacious means for securing aplurality of spaced bonded abrasive sectors in fixed relation to eachother on a rigid backing member. A hard rubber of this general type hasbeen found to readily adhere directly to an iron supporting platewithout necessitating any special preparation of the plate or the rubbercompound itself aside from that of adequately cleaning and slightlyroughening the surface of the backing plate by any suitable method, suchas a sand-blasting operation.

Similarly, it has been found that rubber, commonly'known as softrubber", containing 5% or less of combined sulphur by weight and whichis vulcanized to a soft, resilient, deformable condition, may also beemployed to cement a plurality of abrasive sectors to a suitable rigidbacking member.

The interstices between the spaced abrasive sectors may be filled withany suitable cementitious material, such as a hard or soft rubber orother suitable vulcanizable compounds which will permanently adhere tothe adjacent opposed sectors and alsoto the layer of rubber compoundwhich secures the sectors to the backing member; or, if desired, theinterstices between the adjacent sectors may be partially filled leavingthe operative wheel face interrupted by a series of narrow grooves,whereby the individual sector faces may be free to expand during thegrinding operation. In any event, thematerial be tween the adjacentsectors is so composed or so positioned that expansions and contractionsof each operative sector face may be compensated for withouttransmitting stresses and strains to Other portions of the grindingdisk.

Since the material between the adjacent opposed abrasive sector faces iscomposed of a vul canizable compound, it will integrally unite with thelayer of rubber compound securing the abrasive disk to the backingmember, and thereby further aid in securing the abrasive sectorsintegrally with the backing member and in correct grinding position. A.grinding disk of this type may be manufactured in any convenient sizeand its operative grinding face which is often subjected to excessivelyhigh temperatures of grinding will be free to expand and contractwithout setting up internal wheel stresses which tend to cause wheelbreakage in prior types of grinding disks.

As illustrated, the preferred type of my invention comprises a diskshaped grinding wheel III, of any desired diameter and thickness,composed of a plurality of spaced bonded abrasive sectors I2, which areseparately manufactured and assembled in the form of an annulus having asubstantially continuous fiat grinding face I4, outer and innerperipheral faces I5 and I6, respectively, and a supporting face II. Inthe present instance, for convenience of illustration, my grinding diskis shown composed of six separately manufactured bonded abrasivesectors, but it will be appreciated that any number of sectors may beemployed within the scope of this invention. Each of these sectors iscomposed of abrasive grains, such as crystalline alumina or siliconcarbide, suitably bonded together into the desired shape by vitrifiedceramic materials, rubber, resinoids, sodium silicate, or other suitablebonding materials that are well known in the art. Each sector is furtherprovided with two converging side faces I8 which, in my preferredconstruction, are substantially perpendicular to the operative grindingface and substantially radial of the assembled grinding disk.

The sectors are permanently secured and evenly supported in grindingposition by means of a backing member 20 composed of any suitable rigidmaterial. As illustrated in my preferred construction, this backingmember may comprise a substantially fiat, thin, circular iron plate ofthe same diameter as the disk periphery I5, and of such thickness thatit will rigidly and evenly support the abrasive sectors during agrinding operation.

The backing member is provided with a supporting face 22,.which is shownas substantially flat and arranged to be integrally secured to thebonded abrasive disk supporting face I1 by means of an intermediatelayer of a suitable vulcanizable rubber compound 23, which is relativelythin in comparison to the thickness of the backing plate. This layer ofrubber compound is vulcanized in position under the influence ofsuitable heat and pressure. The term "rubber as used in the claims alsorelates to any vulcanizable material, such as various syntheticmaterials of the general behavior of rubber or rubber containing variousfillers, etc. The term hard rubber as specified in various claimsrelates specifically to any vulcanizable rubber compound containing atleast 20% of combined sulphur by weight and which will vulcanize into ahard, substantially non-resilient body of the type of ebonite orvulcanite. The term soft rubber relates to any rubber compoundcontaining 5% or less of combined sulphur by weight and which willvulcanize into a soft, resilient, deformable, tough material. Theinterstices between the adjacent opposed sector faces l8 may be. filledwith any suitable vulcanizable material, such. as a rubber compound 25,which may be vulcanized in position and will adhere to the opposed facesl8, and unite with the rubber compound 23, permanently securing saidmembers together and thereby aiding in forming the abrasive sectors intoan integrally united annulus.- In my preferred construction, this rubbercompound 25 is preferably of such a composition that it may deformslightly during the grinding operation and thereby compensate for anyexpansions or contractions of the operative grinding face I occasionedby the frictional heat of grinding, so that the stresses and strainswithin any of the individual sectors may be compensated for and nottransmitted throughout the entire-grinding disk. It will be appreciatedthat the rubber compound 25 may or may not be of the same composition asthat of the rubber compound 23. In any event, the layer of rubberbetween the adjacent sectors should be so positioned or of such acomposition that the individual sector grinding faces may be free tobreathe or expand and contract towards and from one another under theinfluence of the frictional heat of grinding.

If desired, a modified form of my invention, as

' shown in Fig. 3, may embody a similar disk construction wherein theinterstices between the ad-. jacent opposed sector faces I8 arepartially filled with a layer of vulcanizable rubber compound 21 in sucha manner that the operative grinding face I4 is interrupted by a seriesof spaced narrow grooves which permit expansions and contractions of theindividual sector grinding faces. The intervening layers of rubbercompound 21 are vulcanized in position and serve to integrally unitewith the rubber compound 23, as well as to aid in securing the sectorsl2 together as an integral grinding annulus 31 the same manner as in mypreferred construction.

Any suitable devices may be employed to removably fasten the diskassembly to any convenient rotatable support in grinding position. Onemethod of accomplishing this comprises a series of countersunk holes 26passing through the backing plate, as shown, whereby screws 28 may beemployed to removably mount the backing plate on any suitable rotatablesupporting member 30. The backing member 20 may be further provided witha central aperture 32 adapted to slidably fit over a protruding hub 33projecting from the end of the rotatable supporting member 30 which aidsin axially locating the disk relative to its support. It will beappreciated, of course, that any one of many various well-known devicesmay be utilized to removably clamp the backing plate 20 to any suitablerotatable support in any convenient manner to perform a grindingoperation.

In the construction of my invention, the backing plate has itssupporting face 22 suitably .cleaned and roughened by any convenientmethod such, for example, as a well-known type of sandblastingoperation. If desired, the supporting face may be further provided withsuitable channels, reentrant grooves or holes which will aid the rubbercementing compound in firmly gripping the back plate. A suitable layerof raw plastic rubber compound 23 containing the desired amount ofsulphur and, if desired, a suitable vulcanization accelerator is cut inthe shape of an annulus having the same outer and.inner diameter as thegrinding annulus l0 and then placed upon surface 22. The bonded abrasivesectors l2 are then placed in spaced relation upon the layer of rubbercompound 23 in the form of an annulus whose periphery coincides withthat of the backing plate 20. A layer of suitable rubber compound 25 or21 is then placed within the interstices between each of the opposedsegment faces ill in such a manner that it either entirely or partiallyfills each of said crevices, as the case may be in accordance with the 7type of grinding'disk desired. The abrasive sectors and backing memberare thereafter clamped together in any suitable mannerand sufiicientheat, such as 200 or 250 C., is applied for a desired period tovulcanize all of the rubber compounds in position and secure theabrasive sectors and backing member into an integral unitary tegrallysecured to the rubber 23 and the sectors l2 ,by a subsequent vulcanizingoperation. It will be appreciated that the rubber compound 23 willvulcanize in position and serve to intimately unite the surface I! ofthe abrasive disk and surface 22 of the backing member, since itsecurely adheres to both of said surfaces. By applying various clampingpressures between the abrasive sectors and the backing plate, theintervening layers of rubber compounds may be caused to impregnate thesurfaces l1 and I8 of the grinding disk to any desired extent andthereby secure it to the backing plate with the required tenacity.

While I have specifically described my invention as particularly adaptedto a sector type of abrasive wheel arranged to grind with its flat face,it will be appreciated by'those skilled in the art that various otherabrasive articles may be easily produced and secured to backing platesor supporting members in the same manner. Such modifications orsubstitutions of this invention 'as lie within the. scope of theappended claims are,

ing faces and flat grinding faces which are ar-v ranged to provide anextensive, substantially flat grinding surface, a rigid backing membertherefor, a layer of (rubber compound vulcanized in position between thebacking and the supporting faces and serving alone to secure thesegments to the backing, and deformable rubber compound vulcanized inposition within. the spaces be tween each of the adjacent sectors, saidvulcanized rubber compounds securing the sectors and backing together asan integral grinding unit and compensating for expansions andcontractions of the grinding iaces under the influence oi frictionalheat of grinding.

2. A grinding disk comprising a plurality of separately manufacturedbonded abrasive sectors having flat grinding faces arranged in closelyspaced relationship to each other to provide an extensive, substantiallycontinuous, flat annular grinding face, a rigid, disk shaped metalbacking plate therefor adapted to support the abrasive sectors, a layerof rubber compound vulcanized in position between the sectors and thebacking plate and serving alone to secure the segments on the plate, adeformable rubber compound partially filling the interstices betweenopposed side faces of adjacent abrasive sectors and vulcanized inposition to aid in securing the sectors together as an integral grindingunit and yet leave the outer portions of the sectors separated by freespaces and permit expansion and contraction of the grinding face, andmeans to removably secure the backing plate to a rotatable support.

3. A grinding wheel comprising a rigid backing plate having a planemounting surface, a plurality of separately manufactured, vitrifiedbonded abrasive sectors having plane supporting faces and opposed planegrinding faces which are secured to the backing plate in a widely spacedrelationship but provide an extensive annular grinding face extendingfrom near the axial center of the backing plate to its periphery, alayer of rubber compound vulcanized inposition between the backing andthe adjacent sector faces and serving alone to secure the sectors to thebacking plate, a deformable rubber compound completely filllng thespaces between the opposed side faces of adjacent abrasive sectors whichis vulcanized in position and unites the sectors as an integral grindingunit and yet per-' mits expansion and contraction thereof, and meansaccessible within the hole of thewheel for removably securing thebacking plate to a rotatable support.

THURE L. F. LARSSON.

